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The characteristics and working principles of UC3637 dual PWM controller and IR2 1 10 are briefly analyzed. UC3637 and IR2110 * *+00 * * construct a high voltage, high power and small signal amplification circuit, and its feasibility is verified by experiments.
Keywords: small signal amplifier; Double pulse width modulation; Suspension drive; High voltage and high power
introduce
Many existing small signal amplification circuits are composed of transistors or MOS transistors, and their power is limited, so the power of the circuit cannot be made very large. With the gradual maturity of modern inverter technology, especially SPWM inverter technology, the signal waveform can be well reproduced at the output end to realize high voltage, high current and high power. There are two ways to realize SPWM technology. One is that the analog integrated circuit compares the sine modulated wave with the triangular wave carrier to generate SPWM signal. The other is to use the numerical method. With the deepening of application and the development of integration technology, commercial application specific integrated circuit (ASIC), special single chip microcomputer (8X 196/MC/MD/MH) and DSP can simplify the control circuit structure and achieve high integration. Because digital chips are generally expensive, analog integrated circuits are used here. The main circuit adopts full-bridge inverter structure, and the generation of SPWM wave adopts UC3637 dual PWM control chip, and adopts the high-voltage floating drive integrated module IR2 1 10 imported from American IR company, which reduces the volume of the device, reduces the cost and improves the reliability of the system. After being amplified by this circuit, the signal can reach 3kV and keep a good output waveform.
Figure 1
Principle and basic function of 1 UC3637
The principle block diagram of UC3637 is shown in figure 1. It includes a triangular wave oscillator, an error amplifier, two PWM comparators, an output control gate, a pulse-by-pulse current-limiting comparator and so on.
UC3637 can work with single power supply or dual power supply, and its working voltage range is (2.5 ~ 20) V, which is especially beneficial to bipolar modulation. Bidirectional PWM signal, totem pole output, providing or absorbing current capacity100ma; ; Pulse-by-pulse current limiting; Built-in constant amplitude triangular wave oscillator with good linearity; Undervoltage blockade; Temperature compensation; 2.5V threshold control.
The most remarkable feature of UC3637 is the triangular wave oscillator, and the triangular wave generating circuit is shown in Figure 2. Triangular wave parameters are calculated according to formula (1) and formula (2).
Is=[(+VTH)-(-Vs)]/RT ( 1)
f=Is/{2CT[(+VTH)-(-VTH)]} (2)
Where: VTH is the turning point (threshold) voltage of the triangle peak;
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Design of FM Wireless Transmitting Circuit Based on BH 14 17 Chip
introduce
BH 14 17 is an FM wireless transmitter chip. It can work in the frequency band of 87 MHz ~ 108 MHz, and can transmit audio FM signals with simple peripheral circuits. It can transmit stereo audio signals such as computer sound card, game machine, CD, DVD, MP3 and mixer through stereo modulation, and can realize wireless FM stereo transmission with ordinary FM stereo receiver. It is suitable for producing wireless audio adapters such as stereo wireless speakers, wireless headphones, CDs, MP3, DVDs, PADs and notebook computers.
Principle and characteristics of BH 14 17
Frequency modulation transmitting circuit adopts phase-locked loop system, and the frequency is stable. This part consists of high frequency oscillator, high frequency amplifier and PLL frequency synthesizer. Frequency modulation is realized by a high-frequency oscillator composed of varactor diodes. The high-frequency oscillator is the VCO of the phase-locked loop, through which the stereo composite signal is directly frequency modulated. The high-frequency oscillator consists of an LC loop outside the ninth pin and an internal circuit. The oscillation signal is output from pin 1 1 through the high-frequency amplifier, and sent to the phase-locked loop circuit for comparison, and then the signal output from pin 7 corrects the value of the high-frequency oscillator to ensure the frequency stability. Once the frequency set by PLL is exceeded, the seventh pin will pull the output level high; If it is lower than the set frequency, the output level will be reduced; At the same time, its level will not change.
1) integrates pre-emphasis circuit, amplitude limiter circuit and low-pass filter circuit (LPF), which greatly improves the quality of audio signal compared with circuits with discrete components (such as BA 1404, NJM2035, etc.). ).
2) PLL is used to lock the frequency, and it is integrated with FM transmitting circuit to make the transmitting frequency very stable.
3) The frequency setting adopts a 4-bit pull code switch, which can set 14 frequency points, making it very convenient to use.
The internal structure of BH 14 17 is shown in figure 1. It consists of five parts: audio preprocessing circuit (emphasis, amplitude limiting and low-pass filtering); Fundamental frequency generation circuit (crystal oscillator, frequency division); PLL circuit (phase detection, frequency locking); Frequency setting circuit (high and low level conversion); Frequency modulation transmitting circuit. The peripheral circuit mainly includes frequency control circuit composed of pull code switch, carrier generation circuit composed of voltage controlled oscillator, timer and some coupling capacitors.
Application circuit
Design of limiting circuit for audio input terminal
BH 14 17 audio input has a maximum volume limit. Excessive input level will damage the chip. In the early experimental stage, the amplitude of input audio level is unpredictable. In order to protect the chip, it is necessary to limit the input audio signal. The limiting circuit is very simple, just use a variable potentiometer. The circuit is shown in Figure 2, in which the capacitor is used to couple the audio signal into the chip and has the function of blocking DC.
Parameter design of voltage controlled oscillator
Combined with BH 14 17, it can be seen that the frequency range of VCO must cover all frequency points of the chip. Considering the accuracy of general components and the level of processing technology, the frequency band is appropriately relaxed here to ensure that the chip can normally lock the frequency point. Suppose the frequency band is 80 MHz ~ 120 MHz. The circuit of voltage controlled oscillator is shown in Figure 3. L adopt common adjustable inductance with magnetic core, and the nominal value of inductance is (30 NH ~ 60 NH); The capacitance of varactor varies with the change of bias voltage, and its limit range is (7pF~35pF). In order to ensure the stability of the circuit, the values of C2 and C3 should not be too different. It is assumed that C2 is 5 1pF, and C3 ranges from 7pf to 35pf. The value of C 1 is determined as follows. From the expressions (1) and (2), it can be seen that when the inductance L and the capacitance C3 are both minimum, the voltage-controlled oscillator obtains the maximum oscillation frequency, and vice versa.
In the above formula, the unit of C 1 is pF. Calculated: 45.27 According to the above calculation, the value of each component is not unique. Here is just a demonstration of the calculation ideas and methods. I hope it can provide theoretical reference for designing circuits.
Design of FM transmitting circuit
Stereo signals are input through pins 1 and 22, and low-pass filtering, pre-emphasis and modulation of stereo signals are completed through the resistance-capacitance combination of pins 2, 3, 20 and 2 1, and the modulated composite signals are output through pins 5. The frequency codes input through pins 15, 16, 17 and 18 are decoded and phase-discriminated, and the control signal VCO of PLL oscillator is output through pin 7. This VCO controls the external high-frequency oscillation circuit composed of discrete components to generate FM modulated carrier signal, and FM modulates the composite stereo signal output by five pins through a Darlington transistor 2SD2 142. The modulated signal is input to BH 14 17 through pin 9, and the RF signal amplified by the internal RF amplifier is output through pin 1 1. The output signal can be directly connected to the transmitting antenna for transmission, or input to the RF power amplifier for amplification and transmission, thus expanding the transmission distance. Pin 13 and pin 14 need an external 7.6MHz crystal oscillator to provide a stable clock for phase detection and stereo signal modulation in BH 14 17.
To sum up, a typical application circuit of BH 14 17 wireless transmitter chip can be obtained, as shown in Figure 4. Users can set the transmission frequency (as shown in table 1) by changing the ON/OFF of the dip switch JP 1 to avoid the interference of strong radio stations in the possible area.
label
BH 14 17 can be used in many products, but the design and control principles of its peripheral circuits are basically the same. The design scheme introduced in this paper can ensure the normal operation of BH 14 17 after practical application, and the design of its voltage-controlled oscillator and RF part can be used for reference or directly applied.